how to mix graphite powder to get shielding paint

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Greg Martin
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how to mix graphite powder to get shielding paint

Post by Greg Martin »

I was given a pound or 2 of graphite powder,and some one said shielding paint could me made. What binder/solvent would be best to make it brushable and to to keep conductivity?

David King
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Re: how to mix graphite powder to get shielding paint

Post by David King »

I don't think I'd waste a lot of effort on this but you could try with some water based varnish and see if you can maintain conductivity. I remember hearing from someone who had tried this and given up on it.

Daryl Kosinski
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Re: how to mix graphite powder to get shielding paint

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Greg Martin
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Re: how to mix graphite powder to get shielding paint

Post by Greg Martin »

well right now I have a large bottle of powder, i dont have copper foil, so Id like to make this resource work.wterbourne finish or maybe shellac or hide glue will be my first testing agents l thanks for the tips.

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Andrew Porter
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Re: how to mix graphite powder to get shielding paint

Post by Andrew Porter »

How about applying a good coat of paint dump in the powder. Empty when dry. Drive a screw through with the grounding wire.
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Eric Baack
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Re: how to mix graphite powder to get shielding paint

Post by Eric Baack »

you can also get foil tape from ebay and amazon for pretty cheap. I've checked continuity on it through the adhesive and it checks out.

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Dan Smith
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Re: how to mix graphite powder to get shielding paint

Post by Dan Smith »

We used zinc paint in the old days to coat electronic frames for grounding.
I use copper foil tape these days, easy to apply.
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Greg Martin
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Re: how to mix graphite powder to get shielding paint

Post by Greg Martin »

Ok thanks anyway guys Like I said Ive bought and used aluminum and copper shielding tape for years,but was given a pound of graphite powder and wondered what the liquid agent was to make it paintable like stewmacs !!! Ive got it, just need to know what its good for. Im going to try waterbased finish and maybe shellac as a liquid agent as a first testing. See what happens.

Gregory nangle
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Re: how to mix graphite powder to get shielding paint

Post by Gregory nangle »

the best thing to do as a graphite expert is to use a mixture of isopropyl alcohol and graphite powder (be sure the powder is truly powder) spray this on and then follow that after it dries with a coat of shellac thinned a bit with denatured,they both use the same airborne finish to dry.must be sprayed! the first coat or two of your mixture will pull off the surface until its sealed in with the shellac.

Gregory nangle
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Re: how to mix graphite powder to get shielding paint

Post by Gregory nangle »

you could also use 'acrylic medium' mixed with graphite powder to brush it on ,thats a more robust finish and probably easier to apply.

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David Schwab
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Re: how to mix graphite powder to get shielding paint

Post by David Schwab »

Gregory nangle wrote:the best thing to do as a graphite expert is to use a mixture of isopropyl alcohol and graphite powder (be sure the powder is truly powder) spray this on and then follow that after it dries with a coat of shellac thinned a bit with denatured,they both use the same airborne finish to dry.must be sprayed! the first coat or two of your mixture will pull off the surface until its sealed in with the shellac.
Wouldn't the shellac act as an insulator? How are you going to make an electrical connection with the paint?

Personally I never found the carbon based paints to work very well, and in most cases there's very little reason to shield control cavities, which is what it's mostly used for.

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Hans Bezemer
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Re: how to mix graphite powder to get shielding paint

Post by Hans Bezemer »

You could make Indian / Chinese ink with it: http://www.ehow.com/how_7370727_homemad ... n-ink.html
I've used Indian ink to stain wood and it shielded well.

Jason Rodgers
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Re: how to mix graphite powder to get shielding paint

Post by Jason Rodgers »

Hans Bezemer wrote:You could make Indian / Chinese ink with it: http://www.ehow.com/how_7370727_homemad ... n-ink.html
I've used Indian ink to stain wood and it shielded well.
Hmm, so you're saying the lampblack in India ink has enough carbon to shield? Can you put a meter on it to show conductivity for grounding? What sort of resistance does it show across a cavity?

If you're going to attempt to mimic India ink, then the traditional binder was hide glue (or so says wikipedia https://en.wikipedia.org/wiki/India_ink).

The graphite grounding paints are pretty nasty, especially if you're trying to go low-VOC in your finishes. India ink would be a hugely less toxic alternative, if it worked as a shielding paint.

EDIT: After reading the wiki article in length, I see that it is in fact used in some shielding applications: Once dry, its conductive properties make it useful for electrical connections to difficult substrates, such as glass. Although relatively low in conductivity, surfaces can be made suitable for electroplating, low-frequency shielding, or for creating large conductive geometries for high voltage apparatuses. A piece of paper impregnated with India ink serves as a grid leak resistor in some tube radio circuits.

I don't understand the electrical engineering application descriptions, but I suppose "relatively low in conductivity" excludes it from use as a cavity shielding paint.
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Gregory nangle
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Re: how to mix graphite powder to get shielding paint

Post by Gregory nangle »

David Schwab wrote:
Gregory nangle wrote:the best thing to do as a graphite expert is to use a mixture of isopropyl alcohol and graphite powder (be sure the powder is truly powder) spray this on and then follow that after it dries with a coat of shellac thinned a bit with denatured,they both use the same airborne finish to dry.must be sprayed! the first coat or two of your mixture will pull off the surface until its sealed in with the shellac.
Wouldn't the shellac act as an insulator? How are you going to make an electrical connection with the paint?

Personally I never found the carbon based paints to work very well, and in most cases there's very little reason to shield control cavities, which is what it's mostly used for.
i use it for electroplating so i cant really speak to its ability to shield. usually we glue down a copper wire to the edge of the paint and then bring paint over that to the bare copper and it conducts enough to plate. for shielding i woudlnt think this is an especially great way to achieve a good shield either but if i had to venture a guess baout what the origianl poster was trying to do that was it. the shellac does not conduct but the particles of graphite suspended(at a great density of course) in it are touching in enough places to conduct. id just use foil and call it day too though! :)

David King
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Re: how to mix graphite powder to get shielding paint

Post by David King »

You don't need a high conductivity for shielding at low frequencies. You do need a solid connection to ground which is usually the more challenging part of the problem. Here's a bit of info on RF shielding that might be useful:
http://www.thermospray.com/faqs/EMIRFI.html

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